1. Field of the Invention
The invention relates generally to the field of acoustical signal processing, more particularly to the detection of arterial stenosis using wavelet transforms and neural networks.
2. Description of Background Art
Coronary artery disease (CAD) is one of the leading causes of death in the world with approximately one third of all deaths attributed to this disease. Accordingly, early detection of coronary artery disease is an important medical research goal.
Several methods exist for the diagnosis of coronary artery disease. These methods can be classified generally as being either noninvasive or invasive. Noninvasive diagnosis methods do not involve penetration of the skin or entry into the body through any natural openings. Noninvasive diagnosis methods include: the physical exam and history method; electro-cardiogram (ECG) techniques such as exercise testing, vectorcardiograms, and apex cardiogram; ultrasound examination, e.g., echocardiography; and imaging examination, e.g., roentgenograms, tomography, and nuclear magnetic resonance. The problem with current noninvasive diagnosis methods is that they have only a moderately successful accuracy rate for diagnosing coronary artery disease.
Invasive diagnosis methods are frequently more reliable than noninvasive diagnosis methods. One of the most reliable technique for diagnosing CAD is cardiac catherization (cath.). In this technique a catheter is inserted into an artery, e.g., a brachial or femoral artery, and advanced to the heart. Once in the heart, dye can be released to observe the coronary arteries. Although direct assessment of a coronary occlusion is conclusive, this technique is expensive, painful, time consuming, and has a significant risk to the patient, e.g., the mortality rates can range from 0.2%-7%.
Another invasive diagnosis method is referred to as the thallium test. In the thallium test, thallium-201, a radio-pharmaceutical substance with biological properties similar to potassium and commercially available, is used to detect myocardial ischemia in patients with CAD. When given invasively, its myocardial distribution is proportional to myocardial blood flow. Therefore, low blood flow regions accumulate less thallium and appear as cold spots on the image obtained from a camera that is located over the precordium. Although the sensitivity of the thallium test is 83%, and its specificity is 90%; it is costly and time consuming to implement.
What is needed is a reliable, inexpensive, noninvasive diagnosis technique that will enable coronary artery disease to be detected at an early stage of development.